The present invention relates to fluorescent particles, a process for producing the fluorescent particles, and anti-falsification paper using the fluorescent particles.
Various kinds of anti-falsification paper containing granular, fibrous or chipped materials having the property of emitting a visible light with a specific wavelength upon irradiation with ultraviolet rays (the property of emitting fluorescence) are known. This anti-falsification paper is characterized in that upon irradiation with ultraviolet rays such as black light, a fluorescent material contained in the paper emits a light with a specific wavelength in the visible-light range, and the specific shape of the fluorescent material is detected whereby whether the paper is falsified or not can be judged.
With respect to anti-falsification paper into which a granular fluorescent material was incorporated, the present applicant proposed, in Japanese Utility Model Laid-Open No. 6500/1994 (Japanese Utility Model Application No. 51094/1992), anti-falsification paper into which fluorescent particles produced by coating paper with a material fluorescing upon irradiation with ultraviolet rays and then shredding the coated paper are incorporated.
Further, anti-falsification paper prepared by fixing an ionic fluorescent dyestuff onto special ionic and heat resistant starch particles and incorporating the starch particles into paper was proposed by the present applicant in Japanese Patent Application No. 23904/1998.
In addition, anti-falsification paper prepared by coating the surface of autohesive particles by a high-speed air flow impact method with a water-insoluble pigment fluorescing upon irradiation with ultraviolet rays and then incorporating the particles into paper was proposed by the present applicant in Japanese Patent Application No. 92477/1998.
The above-described prior art techniques are directed to anti-falsification paper prepared by incorporating a granular fluorescent material in paper. In the anti-falsification paper proposed in Japanese Utility Model Laid-Open No. 6500/1994 among the prior art techniques described above, the fluorescent particles seem to be present in the form of amorphous and fine flocks in the paper, but it is difficult to regulate the size of these particles, and there is the problem that unnecessarily large flocks and unnecessarily small flocks are contained in the paper.
Since the anti-falsification paper proposed in Japanese Patent Application No. 23904/1998 makes use of fluorescent particles using a fluorescent dyestuff, there is the problem that the light resistance is inevitably worsened as compared with fluorescent particles using a fluorescent pigment, and the intensity of fluorescing upon irradiation with ultraviolet rays is also low. Further, there is also the problem that the hue of fluorescence is limited.
Although the fluorescent particles used in the anti-falsification paper proposed in Japanese Patent Application No. 92477/1998 have the advantage that they are superior in light resistance and exhibit a higher intensity of fluorescing by use of a fluorescent pigment than that of fluorescent particles using a fluorescent dyestuff, there is the problem that the production thereof necessitates expensive apparatus, and the production yield is low.
On the other hand, inclusion of the fluorescent pigment itself in paper causes many problems. First, there is the problem that since the particle diameter of a commercial fluorescent pigment is as small as about 0.5 to 3 xcexcm, the presence of individual particles cannot be recognized even if paper containing a few % of fluorescent pigment particles is irradiated with ultraviolet rays in a bright room. To be able to recognize the presence of the fluorescent pigment, the particle size should be increased, but in this case, the pigment with a special particle size should be produced, and thus the price of the usually expensive fluorescent pigment is further raised. In addition, since the specific gravity of the inorganic fluorescent pigment is as high as 4 to 5, there arises the problem that, if paper making is conducted using a pulp slurry containing the pigment with a large particle diameter, the fluorescent pigment is precipitated in the slurry during transfer thereof.
This invention was made under these circumstances, and the object of this invention is to provide completely novel fluorescent particles and a process for producing the same, as well as anti-falsification paper prepared by inclusion of the fluorescent particles in the paper so that the particles fluorescing in various hues with unique cylindrical or spherical shapes can be clearly visually recognized upon irradiation with ultraviolet rays and are further excellent in light resistance.
The fluorescent particles according to the present invention comprise granules of a mixture of a water-insoluble dyestuff and/or pigment fluorescing upon irradiation with ultraviolet rays (also referred to hereinafter as xe2x80x9cfluorescent dyestuffxe2x80x9d and xe2x80x9cfluorescent pigmentxe2x80x9d or as xe2x80x9cfluorescent agentxe2x80x9d when the two are generally named) and a powdery material; and the fluorescent particles can be produced by mixing the fluorescent dyestuff and/or the fluorescent pigment with the powdery material and then granulating the mixture.
Further, the fluorescent particles of the present invention comprise granules of a powdery material and a coating layer of a fluorescent dyestuff and/or a fluorescent pigment formed on the surface of the granules; and the fluorescent particles can be produced by granulating the powdery material and then coating the surface of the granules with the fluorescent dyestuff and/or the fluorescent pigment.
Further, the fluorescent particles of the present invention comprise granules of a mixture of a fluorescent dyestuff and/or a fluorescent pigment, a powdery material and a white pigment; and the fluorescent particles can be produced by mixing the fluorescent dyestuff and/or the fluorescent pigment, the powdery material and the white pigment and then granulating this mixture.
Further, the fluorescent particles of the present invention comprise granules of a mixture of a powdery material and a white pigment and a coating layer of a fluorescent dyestuff and/or a fluorescent pigment formed on the surface of the granules; and the fluorescent particles can be produced by granulating a mixture of the powdery material and the white pigment and then coating the surface of the granules with the fluorescent dyestuff and/or the fluorescent pigment.
Further, the fluorescent particles of the present invention comprise granules of a powdery material, a coating layer of a white pigment formed on the surface of the granules and a coating layer of a fluorescent dyestuff and/or a fluorescent pigment formed in the outside of the coating layer of the white pigment; and the fluorescent particles can be produced by granulating the powdery material, then coating the surface of the granules with the white pigment, and coating the outside of the coating layer of the white pigment with the fluorescent dyestuff and/or the fluorescent pigment.
In the present invention, a resin binder having 2 or more reactive groups reacting with the hydroxyl groups of the powdery material may be used in granulation or coating, whereby water-resistant fluorescent particles can be produced.
That is, the water-resistant fluorescent particles of the present invention comprise granules of a mixture of a powdery material having hydroxyl groups, a fluorescent dyestuff and/or a fluorescent pigment, and a resin binder having 2 or more reactive groups (hereinafter referred to simply as resin binder) reacting with the hydroxyl groups of the powdery material; and the fluorescent particles can be produced by mixing the powdery material, the fluorescent dyestuff and/or the fluorescent pigment and the resin binder and then granulating the mixture.
Further, the water-resistant fluorescent particles of the present invention comprise granules of a mixture of a powdery material having hydroxyl groups, a white pigment, a fluorescent dyestuff and/or a fluorescent pigment, and a resin binder; and the fluorescent particles can be produced by mixing the powdery material, the white pigment, the fluorescent dyestuff and/or the fluorescent pigment and the resin binder and then granulating the mixture.
Further, the water-resistant fluorescent particles of the present invention comprise granules of a powdery material having hydroxyl groups and a coating layer of a mixture of a fluorescent dyestuff and/or a fluorescent pigment and a resin binder formed on the surface of the granules; and the fluorescent particles can be produced by granulating the powdery material and then coating the surface of the granules with the fluorescent dyestuff and/or the fluorescent pigment by the resin binder.
Further, the water-resistant fluorescent particles of the present invention comprise granules of a mixture of a powdery material having hydroxyl groups and a white pigment and a coating layer of a mixture of a fluorescent dyestuff and/or a fluorescent pigment and a resin binder formed on the surface of the granules; and the fluorescent particles can be produced by mixing and granulating the powdery material and the white pigment and then coating the surface of the granules with the fluorescent dyestuff and/or the fluorescent pigment by the resin binder.
Further, the water-resistant fluorescent particles of the present invention comprise granules of a powdery material having hydroxyl groups, a coating layer of a white pigment formed on the surface of the granules, and a coating layer of a mixture of a fluorescent dyestuff and/or a fluorescent pigment and a resin binder formed in the outside of the coating layer of the white pigment; and the fluorescent particles can be produced by granulating the powdery material, then coating the surface of the granules with the white pigment, and coating the outside of the coating layer of the white pigment with the fluorescent dyestuff and/or the fluorescent pigment by the resin binder.
Further, in the present invention, the interaction between an anionic or cationic binder contained in the granules and a cationic or anionic material contained in the coating layer in the step of granulation or coating can be utilized to produce water-resistant fluorescent particles.
That is, the water-resistant fluorescent particles of the present invention comprise granules of a mixture of a powdery material and an anionic binder and a coating layer of a mixture of a fluorescent dyestuff and/or a fluorescent pigment and a cationic material formed on the surface of the granules; and the fluorescent particles can be produced by granulating the powdery material by the anionic binder and then coating the surface of the granules with the fluorescent dyestuff and/or the fluorescent pigment by the cationic material.
Further, the fluorescent particles of the present invention comprise granules of a mixture of a powdery material, a white pigment and an anionic binder and a coating layer of a mixture of a fluorescent dyestuff and/or a fluorescent pigment and a cationic material formed on the surface of the granules; and the fluorescent particles can be produced by granulating the powdery material and the white pigment by the anionic binder and then coating the surface of the granules with the fluorescent dyestuff and/or the fluorescent pigment by the cationic material.
Further, the fluorescent particles of the present invention comprise granules of a mixture of a powdery material and a cationic binder and a coating layer of a mixture of a fluorescent dyestuff and/or a fluorescent pigment and an anionic material formed on the surface of the granules; and the fluorescent particles can be produced by granulating the powdery material by the cationic binder and then coating the surface of the granules with the fluorescent dyestuff and/or the fluorescent pigment by the anionic material.
Further, the fluorescent particles of the present invention comprise granules of a mixture of a powdery material, a white pigment and a cationic binder and a coating layer of a mixture of a fluorescent dyestuff and/or a fluorescent pigment and an anionic material formed on the surface of the granules; and the fluorescent particles can be produced by granulating the powdery material and the white pigment by the cationic binder and then coating the surface of the granules with the fluorescent dyestuff and/or the fluorescent pigment by the anionic material.
As described above, the fluorescent particles of this invention can be divided roughly into two types, namely a mixture type prepared by granulating a mixture containing all particle constituent components such as the powdery material and the fluorescent dyestuff and/or the fluorescent pigment, and a core-shell type prepared by coating the outside of granules containing the powdery material with a coating layer containing the fluorescent dyestuff and/or the fluorescent pigment. The particles of the mixture type are advantageous for simple production, but from the viewpoint of fluorescence emission, the fluorescent dyestuff and fluorescent pigment present near the surface of the granules emit fluorescence, but those present in the inside of the particles tend to hardly emit fluorescence. On the other hand, in the particles of the core-shell type, the fluorescent dyestuff and fluorescent pigment are present in only the coating layer outside the core granules, and thus all of them will contribute to fluorescence emission. Accordingly, if the same amount of a fluorescent dyestuff or fluorescent pigment is used, the particles of the core-shell type are advantageous over the particles of the mixture type in the respect that a higher intensity of fluorescence emission can be achieved.
By use of the fluorescent particles of this invention described above, anti-falsification paper which is hardly falsified can be obtained. That is, the anti-falsification paper of this invention is characterized by permitting the above-described fluorescent particles to be contained in paper, or by coating the surface of paper with a coating solution containing the above-described fluorescent particles. In such anti-falsification paper, the fluorescent particles cannot be visually recognized or is hardly visually recognized under normal light (usual light such as natural light, light from an incandescent lamp and light from a fluorescent lamp), but upon irradiation with ultraviolet rays, the particles emit fluorescence, thus making it possible to judge whether the paper is an original or an imitation.